The goal of this research is to develop methods for the precise modification of specific target genes in two important genetic model organisms, the nematode Caenorhabditis elegans and the zebrafish Danio rerio. Both nematodes and fish are powerful experimental systems that combine elegant developmental biology with large scale genetics. Both systems have contributed to our understanding of fundamental problems in cancer biology, including programmed cell death, the control of organogenesis, the interaction of cancer susceptibility genes with the environment, and the genetics of melanoma. An important limitation of these model systems is that techniques for site-specific manipulation of the genome are not currently available in either nematodes or fish. Thus, in contrast to murine embryonic stem cells and the yeast S. cerevisiae, it is not possible to knock out specific genes or to precisely control the time and place of gene expression. In the last two years, a powerful new approach to gene-targeting has been developed and successfully used in flies and in mammalian somatic cells. This technique uses chimeric zinc finger nucleases to stimulate precise targeting of specific genes in their native genomic context. The aim of this proposal is to induce targeted, heritable genetic changes via zinc finger nuclease-mediated homologous recombination in C. elegans and D. rerio. Initially we will employ a well-characterized zinc finger nuclease that recognizes the green fluorescent protein (GFP) gene. We will introduce the nuclease into transgenic nematodes and zebrafish that express GFP. We expect the resulting double-strand DNA breaks to stimulate mutagenic non-homologous end joining (NHEJ), leading to the loss of GFP signal. In the second phase, we will simultaneously introduce the nuclease and a repair template that will allow us to create precise mutations in the target locus by homologous recombination. Based on the success of this work we will then target native genes in the worm and the fish by designing novel nucleases and testing them in vitro and in vivo for activity against the targeted gene. We expect that, if successful, this novel approach would be a practical, flexible, and powerful technique that would find wide application, significantly increasing the power of these systems to illuminate human cancer biology. [unreadable] [unreadable] [unreadable]